We report a detailed analysis of optical properties of single submonolayer InAs structures grown on GaAs(001)matrix.It is shown that the formation of InAs dots with 1 monolayer(ML)height leads to localization of excit...We report a detailed analysis of optical properties of single submonolayer InAs structures grown on GaAs(001)matrix.It is shown that the formation of InAs dots with 1 monolayer(ML)height leads to localization of exciton under certain submonolayer InAs coverage,which play a key role in the highly improved luminescence efficiency of the submonolayer InAs/GaAs structures.展开更多
We present photoluminescence studies on highly dense two-dimensional electron gases in selectively Siδ-doped GaAs/ln_(0.18)Ga_(0.82) As/Al_(0.25)Ga_(0.75),As quantum wells(Ns=4.24 × 10^(12) cm^(-2)).Five well-re...We present photoluminescence studies on highly dense two-dimensional electron gases in selectively Siδ-doped GaAs/ln_(0.18)Ga_(0.82) As/Al_(0.25)Ga_(0.75),As quantum wells(Ns=4.24 × 10^(12) cm^(-2)).Five well-resolved photoluminescence lines centered at 1.4194,1.4506,1.4609,1.4695 and 1.4808eV were observed,which are attributed to the subband exciton emission.The subband separations clearly exhibit the feature of a typical quantum well with triangle and square potential.These very intensive and sharp luminescence peaks with linewidths of 2.2 to 3.5meV indicate the high quality of the structures.Their dependence on the excitation intensity and temperatures are also discussed.展开更多
Quantitative reconstructions of atmospheric CO2 by using terrestrial and marine records are critical for understanding the so-called ＂greenhouse＂ conditions in the Cretaceous, but data from terrestrial plants for se...Quantitative reconstructions of atmospheric CO2 by using terrestrial and marine records are critical for understanding the so-called ＂greenhouse＂ conditions in the Cretaceous, but data from terrestrial plants for several stages of this period remain quite limited. Using the stomatal index （SI） technique, here we estimate the Santonian （Late Cretaceous） CO2 contents based on a sequence of fossil cuticles of Ginkgo adiantoides （Ung.） Heer from three beds of the Yong＇ancun Formation in Jiayin, Heilongjiang Province, northeastern China. By the regress function, Sis of Ginkgo fossils reveal a pronounced CO2 reduction from the early to late Santonian （-661 and -565 ppm, respectively）. The relatively high CO2 levels provide additional evidence for paleoclimatic warmth in this interval. Moreover, available paleobotanical data illustrate a decline trend of CO2 contents throughout the Late Cretaceous, punctuated by several fluctuations in particular episodes with different magnitudes. The CO2 contents shifted notably in the late Cenomanian, Turonian, early Santonian, late Campanian, and probably latest Maastrichtian. Furthermore, a comprehensive study based on CO2 data shows that the global mean land surface temperature （GMLST） fluctuated several times accordingly. The change ratios of GMLST （AT） increased from -3℃ in late Cenomanian to -4.7℃ in mid Turonian, and then dramatically reduced to -2.2℃ in mid Coniacian. From the Santonian onward, it appears that the temperature gradually decreased with a few minor fluctuations.展开更多
文摘We report a detailed analysis of optical properties of single submonolayer InAs structures grown on GaAs(001)matrix.It is shown that the formation of InAs dots with 1 monolayer(ML)height leads to localization of exciton under certain submonolayer InAs coverage,which play a key role in the highly improved luminescence efficiency of the submonolayer InAs/GaAs structures.
文摘We present photoluminescence studies on highly dense two-dimensional electron gases in selectively Siδ-doped GaAs/ln_(0.18)Ga_(0.82) As/Al_(0.25)Ga_(0.75),As quantum wells(Ns=4.24 × 10^(12) cm^(-2)).Five well-resolved photoluminescence lines centered at 1.4194,1.4506,1.4609,1.4695 and 1.4808eV were observed,which are attributed to the subband exciton emission.The subband separations clearly exhibit the feature of a typical quantum well with triangle and square potential.These very intensive and sharp luminescence peaks with linewidths of 2.2 to 3.5meV indicate the high quality of the structures.Their dependence on the excitation intensity and temperatures are also discussed.
基金supported by the National Basic Research Pro-gram of China (Grant No. 2006CB701401)the National Natural Science Foundation of China (Grant No. 41002004)+1 种基金China Postdoctoral Science Foundation (Grant No. 20090451258)the Fund of LPS, Nanjing Insti-tute of Geology and Palaeontology, CAS (Grant No. 103107)
文摘Quantitative reconstructions of atmospheric CO2 by using terrestrial and marine records are critical for understanding the so-called ＂greenhouse＂ conditions in the Cretaceous, but data from terrestrial plants for several stages of this period remain quite limited. Using the stomatal index （SI） technique, here we estimate the Santonian （Late Cretaceous） CO2 contents based on a sequence of fossil cuticles of Ginkgo adiantoides （Ung.） Heer from three beds of the Yong＇ancun Formation in Jiayin, Heilongjiang Province, northeastern China. By the regress function, Sis of Ginkgo fossils reveal a pronounced CO2 reduction from the early to late Santonian （-661 and -565 ppm, respectively）. The relatively high CO2 levels provide additional evidence for paleoclimatic warmth in this interval. Moreover, available paleobotanical data illustrate a decline trend of CO2 contents throughout the Late Cretaceous, punctuated by several fluctuations in particular episodes with different magnitudes. The CO2 contents shifted notably in the late Cenomanian, Turonian, early Santonian, late Campanian, and probably latest Maastrichtian. Furthermore, a comprehensive study based on CO2 data shows that the global mean land surface temperature （GMLST） fluctuated several times accordingly. The change ratios of GMLST （AT） increased from -3℃ in late Cenomanian to -4.7℃ in mid Turonian, and then dramatically reduced to -2.2℃ in mid Coniacian. From the Santonian onward, it appears that the temperature gradually decreased with a few minor fluctuations.
